All U.S. Patent documents and other publication discussed below are herein entirely incorporated by reference.
Techniques for producing substituted benzaldehydes have been practiced for over a century. The primary method followed to formylate substituted benzene was the Gattermann-Koch reaction, developed in 1897. This reaction required the combination of equivalent amounts of aluminum chloride, carbon monoxide, and gaseous hydrogen chloride reacted in the presence of a substituted benzene. The temperature was controlled from 25 to 50.degree. C., and the pressure was kept at 1,000 psig. Such a reaction yielded about 70% of the desired substituted benzaldehyde; however, the utilization of stoichiometric amounts of HCl (even in its gaseous state) and the need for high reaction pressures are highly undesirable from a safety standpoint.
Modifications of the Gattermann-Koch reaction have been developed for specific monoalkyl-substituted benzaldehydes, such as in U.S. Pat. No. 4,622,429 to Blank et al.; however, these modifications do not produce significant amounts of dialkyl- or trialkyl-substituted compounds. In fact, patentees only concern with dialkyl- or trialkyl-substituted compounds are in their inherent production within reactions of monoalkyl-substituted benzenes in these modified Gattermann-Koch processes. There is no teaching nor fair suggestion that any further modifications of patentees' procedures when utilized with di- or tri-substituted compounds would produce extremely high yields of the pure corresponding benzaldehydes. Furthermore, Blank et al.'s methods only produce, at the high end, yields up to 77% for monoalkyl-substituted benzaldehydes.
Another method for formylating alkylated benzenes has been disclosed within U.S. Pat. No. 4,195,040 to Renner. Such a teaching includes the formylation of di- and tri-alkylbenzenes; however, this reference also requires the presence and use of large amounts of gaseous hydrochloric acid. Such methods are thus highly undesirable since high levels of HCl are preferably avoided in industrial scale manufacturing, particularly when in gaseous form.
Another more recent method utilizes an HF-BF.sub.3 medium in which to react substituted benzenes systems with carbon monoxide to formylate such compounds. This method has produced very good yields of the dialkyl-substituted benzaldehydes; however, the HF-BF.sub.3 catalyst presents a significant safety hazard which ultimately adds to the cost of the final product.
Thus, there exists a need to develop a proper formylation reaction for substituted benzenes which produces high yields, does not require the utilization of large amounts of potentially dangerous HCl (or other acid) and other catalysts (and thus is relatively safe to perform), and is highly cost-effective. To date, the prior art has not accorded such an improved substituted benzene formylation procedure.